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Measuring up to 8 m. ( 26 ft.) long, standing over 7 feet tall, and weighing in at as much as 4.4 tons, Pachyrhinosaurus was one of the largest types of ceratopsid (or horned dinosaurs). Unlike other ceratopsids, however, the adult Pachyrhinosaurus didn't have a nose horn to go with the two horns on its brow. Instead, it had a large, wrinkly bone mass covering its nose, earning it its name, which means "thick-nosed lizard."

Pachyrhinosaurus probably lived and traveled in herds for feeding and protection reasons: When one dinosaur spotted a predator, he could alert the rest of the herd. Its primary weapon was its armored skull, which it used for ramming its attackers. When confronted with a predator, Pachyrhinosaurus would lower its head and charge forward, then raise its head up quickly and attempt to wound its opponent. Another distinctive ceratopsid feature--the bony headdress-like frill at its neck--could be used as protection for the rest of the body, which was unarmored and vulnerable.

In the 1980s, an entire herd of Pachyrhinosaurus skeletons was found in Alberta, Canada. Studying these fossils, especially those of baby and juvenile dinosaurs, helped paleontologists determine that the disappearance of the Pachyrhinosaurus nose horn in favor of the bulbous nose was not a result of illness, as had previously been thought, but a normal characteristic that developed at the time of puberty.